1. Field of the Invention
The present invention relates to an inspection apparatus for liquid crystal display devices and an inspection method using the same, and more particularly, to an inspection apparatus and inspection method for liquid crystal display devices, wherein a final inspection for completely manufactured liquid crystal display devices is performed using a visual-light inspection apparatus, whereby high productivity due to improved inspection accuracy and reduced inspection time can be accomplished.
2. Discussion of the Related Art
Information-dependent society stresses the importance of display devices as visual information transfer media, and many kinds of flat panel display devices have been developed.
Flat panel display devices include Liquid Crystal Display (LCD) devices, Field Emission Display (FED) devices, Plasma Display Panels (PDPs), Electro-Luminescent (EL) devices, and Organic Light Emitting Diodes (OLEDs), and the like.
Currently, liquid crystal display devices have advantageous characteristics, for example, light-weight, thin-thickness, low power-consumption driving, and the application range of liquid crystal display devices is gradually increasing. According to this trend, liquid crystal display devices are most widely used in laptop computers, office automation equipment, audio/video appliances, indoor/outdoor advertising display apparatuses, and the like. Moreover, by virtue of recently developed mass-production technologies and research and development results, liquid crystal display devices exhibit a rapid development up to a large size and a high resolution.
Such liquid crystal display devices are designed to display an image by adjusting light transmittance of liquid crystal cells according to input image signals.
Now, a method of manufacturing a liquid crystal display device will be described. The manufacturing method comprises: forming a Thin Film Transistor (TFT) array on a lower substrate; forming a color filter array on an upper substrate; bonding the upper and lower substrates to each other; injecting liquid crystals into a gap between the two bonded substrates and sealing the gap to thereby form a liquid crystal panel; testing the liquid crystal panel having the injected liquid crystals and repairing a defective liquid crystal panel; performing a final inspection on a completely manufactured liquid crystal panel according to a predetermined inspection method, to determine whether or not the manufactured liquid crystal panel is a good product or a defective product; and mounting a backlight unit and drive circuits to the liquid crystal panel determined as a good product, to thereby complete the manufacture of a liquid crystal display device.
FIG. 1 is a view illustrating the configuration of a general liquid crystal display device.
Referring to FIG. 1, the liquid crystal display device 1 includes a liquid crystal panel 10 in which a plurality of liquid crystal cells are arranged in a matrix between two upper and lower glass substrates, the liquid crystal panel 10 serving to display an image, a backlight unit 60 to irradiate light to the liquid crystal panel 10, and drivers 20, 30, 40 and 50 to apply drive signals required to drive the liquid crystal panel 10.
The liquid crystal panel 10 includes thin film transistors (hereinafter, referred to as TFTs) formed at intersections of a plurality of gate lines GL1 to GLn and a plurality of data lines DL1 to DLm extending orthogonal to each other, and the liquid crystal cells connected to the TFTs. The TFTs serve to supply image data, supplied from the data lines DL1 to DLm, to the liquid crystal cells, in response to scan signals supplied from the gate lines GL1 to GLn.
The liquid crystal cells include common electrodes and pixel electrodes connected to the TFTs, the common electrodes and the pixel electrodes being arranged to oppose each other with liquid crystals interposed therebetween. With this configuration, the liquid crystal cells can be said to be equivalent to liquid crystal capacitors Clc. In addition, the liquid crystal cells include storage capacitors Cst to maintain a data voltage charged in the liquid crystal capacitors Clc until a next data voltage will be charged. A common voltage Vcom is supplied to the common electrodes of the liquid crystal cells. Meanwhile, in the case of an in-plane switching (IPS) mode liquid crystal display device, common electrodes are formed on a lower substrate.
FIG. 2 is a flow chart illustrating manufacturing processes of a liquid crystal panel. Now, the manufacturing processes of the above-described liquid crystal panel 10 will be described with reference to FIG. 2.
The manufacturing processes of the liquid crystal panel 10 may broadly consist of a TFT array process for forming driving elements on a lower substrate, and a color filter array process for forming color filters and cells on an upper substrate.
First, in the TFT array process (S101), a plurality of gate lines and data lines are formed on the lower substrate, to define pixel areas, and TFTs as driving elements are formed at the respective pixel areas such that the TFTs are connected to both the gate lines and data lines. In addition, pixel electrodes are formed in the TFT array process. The pixel electrodes serve to drive a liquid crystal layer upon receiving signals applied thereto through the TFTs.
In the color filter array process (S104), a color filter layer, which consists of Red, Green and Blue color filters, and common electrodes are formed on the upper substrate.
Next, after applying alignment films to the respective upper and lower substrates to provide the liquid crystal layer formed between the upper and lower substrates with a predetermined alignment direction, the alignment films are subjected to a rubbing process (S102 and S105).
Thereafter, spacers are distributed over the lower substrate, to maintain a constant cell gap (S103). Then, after applying a sealant to an outer rim of the upper substrate (S106), both the upper and lower substrates are bonded to each other under pressure, to form a liquid crystal panel (S107).
Both the upper and lower substrates of the liquid crystal panel are formed of glass substrates and therefore, the large-area glass substrates are subjected to a cutting process (S108), thereby being divided into a plurality of liquid crystal panels.
Subsequently, liquid crystals are injected into the respective liquid crystal panels, and then, liquid crystal injection ports of the respective liquid crystal panels are sealed, to form a liquid crystal layer (S109). Thereafter, an inspection operation to determine whether or not each liquid crystal panel is efficiently manufactured is carried out (S110).
Drivers to drive the liquid crystal panel manufactured via the above-described method include a gate driver 30, a data driver 20, a timing controller 40, a gamma voltage generator (not shown), and a voltage generator 50. The gate driver 30 is provided with a plurality of gate driver ICs to sequentially supply scan signals to the respective gate lines GL1 to GLn formed in the liquid crystal panel 10. The data driver 20 is provided with a plurality of data driver ICs to convert digital image data into analogue image data and supply the analogue image data to data lines DL1 to DLm so as to synchronize the analogue image data with the scan signals. The timing controller 40 serves not only to align the digital image data input from an external station so as to supply the aligned digital image data to the data driver 20, but also to control driving of the data driver 20, the gate driver 30 and the voltage generator 50. The gamma voltage generator (not shown) supplies a reference gamma voltage to the data driver 20, and the voltage generator 50 supplies drive power to the above-mentioned backlight unit 60 and the respective drivers.
The liquid crystal panel 10 has no self-illumination function and thus, requires light sources such as lamps. Conventionally, to irradiate light to the liquid crystal panel 10, the backlight unit 60, which consists of a plurality of lamps and optical members, is used.
Specifically, the backlight unit 60, used to irradiate light to the liquid crystal panel 10, includes a plurality of lamps to emit light, a diffusing plate (light guide plate) to diffuse light emitted from the plurality of lamps, a reflecting plate (reflecting sheet) to reflect the light emitted from the plurality of lamps toward the liquid crystal panel 10 so as to reduce loss of light, and a plurality of optical sheets to polarize, condense, and diffuse the light from the diffusing plate (light guide plate).
The backlight unit 60 may be classified, according to the arrangement of light sources, into a side-light type and a direct-light type. In particular, in the direct-light type, a plurality of light sources such as fluorescent lamps are arranged on a rear surface of the liquid crystal panel 10, so as to directly irradiate light to an entire surface of the liquid crystal panel 10. The direct-light type has advantages of high uniformity and brightness of light to be irradiated to the liquid crystal panel 10 and thus, is advantageous for use in a large-size liquid crystal display device.
Generally, the light sources of the direct-light type backlight unit 60 are continuously driven to irradiate a uniform intensity of light to an entire rear surface of the liquid crystal panel 10, and the liquid crystal panel 10 displays an image by controlling transmittance of the light irradiated from the light sources.
Once the liquid crystal display device having the above-described configuration is manufactured via the above-described manufacturing processes, prior to completing the manufacture of the liquid crystal display device, the liquid crystal display device is subjected to a final macroscopic inspection with the naked eye, to determine whether the manufactured liquid crystal panel 10 is a good product or a defective product.
FIGS. 3 and 4 are views illustrating a related art inspection method of inspecting the completely manufactured liquid crystal panel.
Referring to FIGS. 3 and 4, in the above-described related art inspection apparatus and inspection method for liquid crystal display devices, the liquid crystal display device 1, which incorporates the backlight unit 60 and the liquid crystal panel 10, is subjected to a macroscopic inspection with the naked eye, to determine whether the liquid crystal panel 10 is a good product or a defective product.
For this, the related art inspection apparatus for liquid crystal display devices includes a carrier 70 to sequentially transport each of a plurality of liquid crystal display devices 1 to a predetermined inspection position close to an inspector, a lifter 80 to move the inspector up and down to facilitate a macroscopic inspection of the liquid crystal panel 10 having a large-size screen, and an upper polarizer 90 to allow the inspector to visually inspect whether or not a certain section of the liquid crystal panel 10 has defects.
In the related art inspection method using the above-described inspection apparatus for the liquid crystal display device 1, first, the liquid crystal display device 1 is moved to the inspection position close to the inspector by operation of the carrier 70. Next, as the backlight unit of the liquid crystal display device 1 is driven, a test image for inspection of the liquid crystal panel 10 is displayed on the liquid crystal panel 10. Thereafter, in a state wherein the upper polarizer 90 for a macroscopic inspection is located in front of the liquid crystal panel 10, the inspector visually inspects whether or not a certain section of the liquid crystal panel 10 has defects while being moved up and down by operation of the lifter 80.
Here, the inspector inspects the presence of defects in a Twisted Nematic (TN) mode and an IPS mode by rotating the upper polarizer 90 for a macroscopic inspection by an angle of 45°, 90° or 180°. The TN mode inspection is used to inspect gap defects of liquid crystal cells and other defects due to impurities, and the IPS mode inspection is used to inspect rubbing defects caused during a rubbing process.
The above-described related art inspection apparatus and inspection method for liquid crystal display devices are based on a macroscopic inspection in which the inspector visually inspects a liquid crystal display device under operation of a backlight unit. However, due to an increasing size of liquid crystal display devices, the above-described related art inspection method has several disadvantages of requiring an extended inspection time required for the inspector to visually inspect defects several times. This consequently deteriorates productivity of liquid crystal display devices.
Furthermore, with the above-described related art inspection apparatus for liquid crystal display devices that depends on visual inspection by the inspector, accurately inspecting fine defects in the unit of pixels is difficult, and different inspection results may occur according to the inspector's skill. In conclusion, it is very difficult to maintain uniform product quality.